OK, let's do this. We've got 1503 and 1403 and we're adding them all together.

Step 1: We'll start by adding the digits 3 & 3 in column 1 and get 6.

Step 2: We'll start by adding the digits 0 & 0 in column 2 and get 0.

Step 3: We'll start by adding the digits 5 & 4 in column 3 and get 9.

Step 4: We'll start by adding the digits 1 & 1 in column 4 and get 2.

So, 1503 + 1403 = 2906.

